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首页> 外文期刊>The Journal of Chemical Physics >Structure, hydrolysis, and diffusion of aqueous vanadium ions from Car-Parrinello molecular dynamics
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Structure, hydrolysis, and diffusion of aqueous vanadium ions from Car-Parrinello molecular dynamics

机译：Car-Parrinello分子动力学研究含水钒离子的结构，水解和扩散

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摘要

A molecular level understanding of the properties of electroactive vanadium species in aqueous solution is crucial for enhancing the performance of vanadium redox flow batteries. Here, we employ Car-Parrinello molecular dynamics simulations based on density functional theory to investigate the hydration structures, first hydrolysis reaction, and diffusion of aqueous V2+, V3+, VO2+, and VO2+ ions at 300 K. The results indicate that the first hydration shell of both V2+ and V3+ contains six water molecules, while VO2+ is coordinated to five and VO2+ to three water ligands. The first acidity constants (pK(a)) estimated using metadynamics simulations are 2.47, 3.06, and 5.38 for aqueous V3+, VO2+, and VO2+, respectively, while V2+ is predicted to be a fairly weak acid in aqueous solution with a pK(a) value of 6.22. We also show that the presence of chloride ions in the first coordination sphere of the aqueous VO2+ ion has a significant impact on water hydrolysis leading to a much higher pK(a) value of 4.8. This should result in a lower propensity of aqueous VO2+ for oxide precipitation reaction in agreement with experimental observations for chloride-based electrolyte solutions. The computed diffusion coefficients of vanadium species in water at room temperature are found to increase as V3+ < VO2+ < VO2+ < V2+ and thus correlate with the simulated hydrolysis constants, namely, the higher the pKa value, the greater the diffusion coefficient. Published by AIP Publishing.
机译：从分子水平上了解水溶液中电活性钒物质的性质对于提高钒氧化还原液流电池的性能至关重要。在这里，我们使用基于密度泛函理论的Car-Parrinello分子动力学模拟来研究300 K下的V2 +，V3 +，VO2 +和VO2 +离子的水合结构，首次水解反应和扩散。结果表明，第一个水合壳V2 +和V3 +都含有六个水分子，而VO2 +则与五个水配体配位，而VO2 +则与三个水配体配位。使用元动力学模拟估算的V3 +，VO2 +和VO2 +水溶液的第一个酸度常数（pK（a））分别为2.47、3.06和5.38，而在含pK（a）的水溶液中，V2 +预计是一种相当弱的酸。 ）值6.22。我们还表明，VO2 +离子水溶液的第一个配位域中氯离子的存在对水水解有重大影响，导致4.8的pK（a）值更高。与基于氯化物的电解质溶液的实验观察结果相一致，这将导致较低的VO2 +水溶液易于发生氧化物沉淀反应。发现室温下水中钒元素的计算扩散系数随V3 +

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